Online ISSN
1751-8792
Print ISSN
1751-8784
IET Radar, Sonar & Navigation
Volume 3, Issue 5, October 2009
Volumes & issues:
Volume 3, Issue 5
October 2009
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- Author(s): J. He and Z. Liu
- Source: IET Radar, Sonar & Navigation, Volume 3, Issue 5, p. 437 –448
- DOI: 10.1049/iet-rsn.2008.0118
- Type: Article
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p.
437
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The authors develop a propagator-based algorithm for two-dimensional (2D) direction finding of electromagnetic sources under spatially correlated noise here. The planar-plus-an-isolated array geometry, first defined by Li et al. (1996) is adopted. The authors propose to replace the planar pressure-sensors in Li et al. (1996) by electromagnetic vector sensors, thus exploiting the benefits inherent in the additional measurements made by a vector sensor. Compared with the algorithm in Li et al. (1996), the presently proposed algorithm can offer closed-form automatically paired azimuth-elevation angle estimates, without costly 2D iterative searching. Moreover, the proposed algorithm can achieve the unambiguous direction estimates with enhanced accuracy by setting the planar electromagnetic vector sensors to space much farther apart than a half-wavelength. Therefore the proposed algorithm constitutes a distinct improvement over (Li et al., 1996) - Author(s): G. Zhao-Zhao ; L. Ya-Chao ; X. Meng-Dao ; W. Genyuan ; Z. Shou-Hong ; B. Zheng
- Source: IET Radar, Sonar & Navigation, Volume 3, Issue 5, p. 449 –460
- DOI: 10.1049/iet-rsn.2008.0082
- Type: Article
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p.
449
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The conventional range instantaneous Doppler (RID) algorithm is a well accepted inverse synthetic aperture radar (ISAR) imaging method for manoeuvring targets. In the RID imaging, the cross-range resolution depends on the instantaneous Doppler of scatterers at the imaging instant. For a high manoeuvring target, the instantaneous Doppler of scatterers may be small at some imaging instants and the satisfactory RID images may not be obtained. On the other hand, a large instantaneous chirp rate is often present for the same scatterer at the same instant for RID imaging. In order to obtain some additional information of a manoeuvring target, a novel ISAR imaging approach, referred to as the range instantaneous chirp (RIC), is proposed based on instantaneous chirp rate of scatterer to provide cross-range resolution. Using the proposed imaging algorithm, with the same received data of RID, a RIC image is generated at the same instant with a different ‘view’. Therefore the RIC image may provide some additional information that is not shown in the RID image. With both the RIC and RID images, a better target recognition and identification can be achieved for high-manoeuvring targets. The proposed RIC algorithm is verified by raw radar data. - Author(s): X. Lv ; M. Xing ; Y. Wu ; S. Zhang
- Source: IET Radar, Sonar & Navigation, Volume 3, Issue 5, p. 461 –473
- DOI: 10.1049/iet-rsn.2008.0168
- Type: Article
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461
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Ground moving target indication (GMTI) is one of the most important applications of the bistatic synthetic aperture radar (SAR) system as well as the monostatic system. An algorithm for moving target detection and location is presented with an azimuth-invariant bistatic multichannel SAR, which consists of one transmitter (channel) and multireceivers (multichannel). The algorithm is based on the discussion of the particularities of the bistatic SAR configuration including coherence improvement and clutter characteristics. Then, the corresponding compensating methods including two-dimensional range-azimuth prefiltering and bistatic differential range correction are proposed to solve these particularities. It is shown that using the compensating methods, the stationary clutter can be suppressed and the moving parameters of ground targets can be estimated accurately. Finally, simulation results demonstrate the effectiveness of the proposed algorithm. - Author(s): N. Liu ; L.-R. Zhang ; X. Liu ; Y. Zhou
- Source: IET Radar, Sonar & Navigation, Volume 3, Issue 5, p. 474 –483
- DOI: 10.1049/iet-rsn.2008.0114
- Type: Article
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p.
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A new joint processing method based on joint covariance matrix fitting is presented for the multibaseline synthetic aperture radar interferometry. This method can make full use of the interferometric information embedded in the joint covariance matrix to estimate the terrain height without eigendecomposition and eigenspace division, and is insensitive to the rank variation of the joint signal subspace. By fitting the sample joint covariance matrix tapered with the coherence matrix, this method can work robustly with a finite sample support, which also makes it possible to recover the detail of terrain profile with a small neighbouring sample support. The results of numerical simulations demonstrate the validation of the proposed method. - Author(s): S. He ; J.-X. Zhou ; H.-Z. Zhao ; Q. Fu
- Source: IET Radar, Sonar & Navigation, Volume 3, Issue 5, p. 484 –492
- DOI: 10.1049/iet-rsn.2008.0192
- Type: Article
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p.
484
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Radar signature produced by micro-motion structures contains movement and structure information which is useful for radar target recognition. For stepped frequency (SF) radar, the Doppler modulation is coupled with the stepped carrier frequency. It shifts and smears the high-resolution range profile and makes it difficult to analyse and extract the micro-motion information from the range profile directly. The authors propose to comprehend the SF radar as a special pulse Doppler radar, and the range profile as a Doppler profile for the convenience of motion analysis. The signature of moving targets for SF radar is analysed from this point of view and the equivalent instantaneous Doppler frequency (EIDF) is introduced. Then, a typical micro-motion, rotation, is taken as an example. The sinusoidal vibration of the peaks in the range profile sequence is explained in detail, especially the relationship between the sinusoid parameters and the rotation parameters. An approach to extract the rotation parameters from the range profile or EIDF spectrum sequence is proposed based on the Hough transform. Simulated and experimental results validate the theoretical analysis and the feature extraction method. - Author(s): J. Wang ; S. Jiang ; J. He ; Z. Liu
- Source: IET Radar, Sonar & Navigation, Volume 3, Issue 5, p. 493 –501
- DOI: 10.1049/iet-rsn.2008.0128
- Type: Article
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The problem of adaptive target detection for airborne multi-input multi-output (MIMO) radars with space–time receivers in the presence of Gaussian interference (including clutter and noise) is studied. Previous work has assumed the interference covariance matrix to be known. The case with unknown covariance matrix is investigated here. By exploiting the low rank property of clutter subspace, generalised likelihood ratio test detector and adaptive matched filter detector with diagonal loading are suggested to improve the detection performance of MIMO radars in limited secondary data case. The closed-form detection probabilities and false alarm probabilities of the two proposed detectors are derived and numerically evaluated. Theoretical analysis and numerical results show the advantages of the proposed detectors. - Author(s): X. Meng ; T. Wang ; J. Wu ; Z. Bao
- Source: IET Radar, Sonar & Navigation, Volume 3, Issue 5, p. 502 –511
- DOI: 10.1049/iet-rsn.2008.0184
- Type: Article
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502
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The clutter characteristics of bistatic airborne radar are more complex than those of monostatic airborne radar. The clutter spectra not only vary severely with range, but also vary with bistatic configuration. The problem of range dependence is more serious in monostatic airborne radar. In this paper, the geometry of arbitrary bistatic airborne radar configuration is firstly analysed, and a formula for Doppler frequency calculation with the variables of azimuth angle and bistatic range is deduced, which is an efficient tool for bistatic clutter analysis. Because of the severe clutter range dependence, the processing of compensation is indispensable in space time adaptive processing (STAP). However, when range ambiguity occurs, the compensation is difficult to be applied to each clutter range cell. To solve this problem, a range ambiguity resolving approach is further proposed by utilising azimuth elements in phased array. Because this approach will result in spatial degrees of freedom (DOF) loss, the overlapped subarray processing is introduced in order obtain enough spatial DOF for STAP. By doing so, the compensation for mitigating range dependence can be applied effectively to bistatic clutter. - Author(s): Y. Liu ; H. Meng ; H. Zhang ; X. Wang
- Source: IET Radar, Sonar & Navigation, Volume 3, Issue 5, p. 512 –520
- DOI: 10.1049/iet-rsn.2008.0033
- Type: Article
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In modern radar systems, using stepped-frequency pulse train is an effective approach to achieve high-range resolution (HRR) with narrow instantaneous bandwidth and low system complexity. However, if the parameters of stepped-frequency (SF) radar (such as single pulse bandwidth, frequency step size and sampling instant) are not prudently designed, ‘ghost image’ phenomenon (also called range ambiguity in some literature) will corrupt the synthetic HRR profiles. The relationship between parameters of the SF radar and the ghost images is provided analytically. A new synthetic range profiling algorithm is developed to generate HRR profiles without ghost images by using the least-squares (LS) estimation. For targets with negligible radial velocities, the new LS profiling algorithm can eliminate the ghost images successfully, and introduces less signal-to-noise ratio loss. With this algorithm, the restriction on the frequency step size is less rigid than the traditional unambiguous criterion. Consequently, a higher range resolution could be obtained. Simulations and field experimental results are also presented. - Author(s): J.M. Muñoz-Ferreras and F. Pérez-Martínez
- Source: IET Radar, Sonar & Navigation, Volume 3, Issue 5, p. 521 –529
- DOI: 10.1049/iet-rsn.2008.0176
- Type: Article
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p.
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Maritime targets are usually involved in complex motions that complicate the generation of focused inverse synthetic aperture radar (ISAR) images and their scaling in cross-range. By assuming some hypotheses that translate to some restrictions in the maritime surveillance scenario, a signal model for the phase history is derived. This function is calculated here using phase gradient autofocus and can be related to the pitch motion of the ship, which may consequently be estimated. The amplitude and the period of this pitch estimate allow us to select imaging times at which the ISAR images are descriptive for classification purposes. The cross-range scaling of these images is also achieved. Simulated data are used to validate the technique and to evaluate its performance when deviations from the nominal scenario are present. Results obtained with live data acquired by a high-resolution radar confirm the effectiveness of the approach. - Author(s): N. Levanon
- Source: IET Radar, Sonar & Navigation, Volume 3, Issue 5, p. 530 –540
- DOI: 10.1049/iet-rsn.2009.0007
- Type: Article
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p.
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At their long-range mode, conventional magnetron-based marine radar use low pulse repetition frequency (PRF) to extend the unambiguous range, and increase the pulse-width to regain the average power. The proposed new waveform maintains narrow pulses and high PRF even at the long-range mode. Range ambiguity is mitigated by periodic ‘yes–no’ coding of the transmitted pulse train. Using narrow pulses improves the range resolution and reduces the radial dimension of the illuminated clutter. - Author(s): D.P. Belcher and N.C. Rogers
- Source: IET Radar, Sonar & Navigation, Volume 3, Issue 5, p. 541 –551
- DOI: 10.1049/iet-rsn.2008.0205
- Type: Article
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p.
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Space-based synthetic aperture radar (SAR) necessarily involves imaging through the ionosphere. At low frequencies (VHF, UHF and L-band) the ionosphere will degrade the SAR image. Previous work has shown that the amount of image degradation strongly depends on the integrated strength of ionospheric turbulence, CkL. The focusing, sidelobes and integrated sidelobe ratio all depend on CkL in a manner that can be directly predicted by a simple analytic theory, which is reviewed and extended to cover any synthetic aperture length. Simulations of the ionosphere, using a thin phase screen parabolic equation approach, are performed under different ionospheric conditions for a number of possible SAR systems and the results compared with the analytic theory. It is concluded that, provided that the scattering is weak, the theory represents a good predictor of SAR performance, even at UHF. The known statistics of CkL can therefore be used to predict the performance of any trans-ionospheric SAR without performing a simulation. - Author(s): M. Greco ; F. Gini ; A. Farina ; L. Timmoneri
- Source: IET Radar, Sonar & Navigation, Volume 3, Issue 5, p. 552 –557
- DOI: 10.1049/iet-rsn.2008.0178
- Type: Article
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p.
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In this study, we compare two radar target direction-of-arrival (DOA) estimation algorithms: the classical moving window (MW) estimator, implemented in many real radar systems and the approximate maximum likelihood (AML) estimator. The first technique exploits multiple detections in the same time-on-target and the second one exploits the fact that the radar antenna mechanical scanning impresses an amplitude modulation on the signals backscattered by the target. Performances of the two estimators are numerically investigated through Monte Carlo simulation and compared in terms of root-mean-square-error (RMSE), probability of detection and probability of target splitting, the latter being defined as the probability of detecting more than one target when instead only one is present in the cell under test. Numerical results show that the AML estimator generally outperforms the classical MW estimator, also in terms of robustness to target splitting.
Computationally efficient two-dimensional direction-of-arrival estimation of electromagnetic sources using the propagator method
ISAR imaging of manoeuvring targets with the range instantaneous chirp rate technique
Azimuth-invariant bistatic multichannel synthetic aperture radar for moving target detection and location
Multibaseline InSAR height estimation through joint covariance matrix fitting
Analysis and extraction of stepped frequency radar signature for micro-motion structure
Adaptive detectors with diagonal loading for airborne multi-input multi-output radar
Bistatic clutter analysis and range ambiguity resolving for space time adaptive processing
Eliminating ghost images in high-range resolution profiles for stepped-frequency train of linear frequency modulation pulses
Pitch estimation for non-cooperative maritime targets in ISAR scenarios
New waveform design for magnetron-based marine radar
Theory and simulation of ionospheric effects on synthetic aperture radar
Direction-of-arrival estimation in radar systems: moving window against approximate maximum likelihood estimator
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